Electrical insulation



trical insulating material.

Patented Apr. 17,1945

UNITED STATES PATENT OFFICE IT 2 2,373,996 I ELECTRICAL msULA'rroN Joseph N. Borglin, Wilmington, DeL, ,assignor to Hercules Powder Company, Wilmington, Del.. a corporation of Delaware No Drawing. Application April 18, 1941, Y Serial No. 389,179 g p 2 Claims.

. therewith. More particularly, it relates'to electrical insulation comprising polymerized rosin. Ordinary rosin or colophony has long been used in electrical insulation, sometimes alone, but usually in admixture with other components which modify its properties. The use of rosin in this field has been subject to very great disadvantages which have not heretofore been overcome. Among these are its objectionable tendency to deteriorate and break down with the passage of time. its amorphous character and its desirable characteristics. Moreover, its low melting point is a serious disadvantage. Another objection is its poor. resistance towater and to moisture'which cause it to 'change to an undesirable material. Still another serious disadvantag of ordinary rosin is its great brittleness and. its lack of resistance to impact and other external forces. The

lack of flexibility and the shattering nature ordinary rosin are very well known. All of these objections have'served todeter the use of .rosin in the electrical insulation field. Numerous efthe use-of rosin in this field because of these undesirable properties. However, these attempts have not been successful because rosin possesses certain properties which cannot be economically duplicated with any other material.

' The principal'object of the present invention is to provide electrical insulation overcoming, to

discovered that polymerized rosin exhibits properties which are greatly superior to rosin in the field of electrical insulation.

Polymerized rosin is rosinwhich has been chemically treated in known manner to polymerize the rosin, and is characterized by a mo-' lecular weight of from about to about-200% In addition, it crystallizes readily, losing greater than ordinary rosin in its pure state, a melting point as determined by the Hercules drop methodabove 85 0., usually at least 100 C., and in general of from about 5 C. to about 100 C. above that of .the untreated ordinary rosin. Polymerized rosin is further characterized by substantial freedom from hardening substances held in combination, aniodlne value lower than that of ordinary rosin, and an acid number ranging from that of the original rosin down to about 100.

In accordance with the present invention, it is preferred touse polymerlzedrosin having a melting point (drop) of at least about 100 C. This polymerized rosinmay have been obtained from acid, phosphoric acid, amphoterlc metal chloforts have been made to dispense altogether with,

ordinary rosinby polymerization with sulfuric rides, etc. followed by separation of catalyst and refining, if desired, in any suitable manner. Typical methods of polymerizing rosin are shown in U. S. patents to Rummel'sburg, Nos. 2,108,928 and 2,136,525 and to Morton No. 2,017,866. I In accordance with the present invention the polymerized rosin may be used by itself as the electrical insulating material in which case it dis-.

a' large, extent, the disadvantages referred to above.

Another objectis to overcome these disadvan tages to a large extent by'the use of a material derived from rosin by a particular chemical treat- Still another object is to provide an improved electrical insulating composition and the combination of a conductor in associationtherewith.

Still other Objects will appear hereinafter.

In accordance with the present invention, the foregoing objects are, in general, accomplished by using polymerized rosin as an electrical insumelting point which makes it less susceptible to Y plays properties considerably improved over ordinary rosin lor such use, such as markedly reducedv tendency to crystallization, reduced tendency to oxidation and deterioration with the passage of time and on exposure to aging influences, a higher temperature changes, improved water resistance which causes it to display improved insulating I characteristics in" humid conditions or. in condi-' tlons where it is exposed to the action of water in liquid form. Other advantages are the greatly reduced shattering tendency of polymerized rosin,

the higher flexibility, and the greater resistance to impacts and other external forces. Polymeriz'ed rosin by itself may advantageously be used in place of ordinary rosin, in, for example, the

' potting of electrical coils and mother fields.

lating material .or in an electricalinsulatlng composition to be used in association with an electrica conductor for insulating the same I have Generally, however, itis preferredto use the p lymerized rosin inadmixture with other mate rials which modify ,its properties. For example,

electrical insulating compositions may be formulated which comprise polymerized rosin incon- Junction with a modifying agent which exerts aplasticlzing or softening action upon the poly-,

merized rosin. Examples of such materials are: oils such as drying oils, for example, tung, linseed, soybean, sunflower, menhaden, semi-drying oils such as corn, cottonseed, rapeseed, etc., non-dryparaihn, ozokerite, Japan wax, beeswax, montan wax, candelllla wax, oamauba wax, synthetic waxes such as, for example, hydrogenated castor oil known in the trade as Opalwax, etc.; or ether and ester plasticizers compatible with the polymerized rosin such as, for example, benzyl ether of glycerine, methyl abietate, ethyl abietate, hydrogenated methyl abietate, acetin, various glyas'zaooo solution in a suitable solvent, or it may be applied to a suitable fibrous backing material such as fabrib or paper or the like which is subsequently applied to the electrical conductor. For example, in accordance with the present invention, polymerized rosin may be used in place of ordinary rosin in the manufacture of varnished cambric. 'Polymerized rosin has also been advantageously employed in the manufacture of electrical insulating colates, butyl stearate, triphenyl phosphate, tri- 2n tape by employing a composition containing th e y p osphate, dibutyl phthalate a d other polymerized rosin with suitable modifiers to a phth l teaet e a o nt of s Substantially suitable fabric backing. varnishes made with non-volatile modifying agent may vary from pglymerjzgd rosin i t of rdjnary msin have about 0.5% to about 25% by weight of the 'combeen advantageously applied in t engmelmg of position and preferably from about to about t copper w u as the lectrical conductor. 15% thereof. The foregoing substances may be In n of these a ph'n flo the polymerized rosin iaggicgfeitlfifesifilglgi 0!; (a: as. $22131 if Si 2 32: readily demonstrites its iigl kgid advantages czar ticularly to reduce the brittleness of the compoggfig yfi g gfii :2; 1:2 1 :5 am; sition while the fatty acids and waxy materials tion l water t also function as iluxing agents togive better com- F magical examples 0f electrical gzgifi gg gi gi ggg g i Wlth other sulating compositions made in accordance with Preferably the g gg E- is used in the present invention. In theseexamples, the combination with another resin, natural or Wm E msm mp-loyed was me by the su-luric acid polymerization of ordinary wood rosin thetic, which is fusible, which has a meltin and had a melting point of about 100 C and an point of at least about 95 C., and an acid number her of 151N155 not over about 150. Examples of such resinous am mun materials are sandarac, red and yellow gum Example 1 accroides, shellac, copalssuch as East African, 40 West African, Sierra Leone, Congo copal, Angola Per cent by We'ght copal, kauri, Boea,'Manilla, pontianak, etc.,.dam- Polymenzed msm 25 mar such as Batavian dammar; etc. Synthetic Shellac resins may be employed such as coumarone in- 18 1 1 (11m) 25 dene resins, oil soluble phenol aldehyde type Tung oil I 6 resins, oil soluble allwds, etc. The amount of. Benzyl ether of glycerine 4 such additional resin will vary considerably depending upon t rm product desired b t in The l'ESlIlS were meltedtogether whereupon the general will fall within the range of from about une oil and th b n yl ether of elycerme were 10% to about 90% of the composition and preferlrre In o h mtur he r l n materlai ably from about 20% to thereof. E p ss s d d n ing properties and displayed G ral y, th amount of polymerized r si m. excellent electrical insulating characteristics.

' Examples 2 to 9 Example No. I j

Per cent Per cent Per cent Per cent Per cent Percent Per cent Per cent by weight by weight by weight by weight by weight by weight by weight by weight Polymerized rosin 44. 44 44. 44 44. 44 44. 44 44- 44 90 50 10 935E133???- Stcaric acid Rapeseed 0 Peanut oil- Sunflower onployed in-the composition will vary between about 10% and about 90% and preferably between about 30% and about For example, compositions'comprising about equal parts by weight of polymerized rosin and ofgum accroides with or without suitable quant ties of the modifying agent referred to above have been found to give extremely satisfactory results.

In each of these formulations, the polymerized rosin and the gum accroides were melted together by heating to -225" C., stirring well and holding until solution has taken place, discontinuing the heating, adding the modifying agents where used, stirring and allowing to cool for subsequent use. Each of the formulations exhibited very satisfactory electrical insulating properties.

Polymerized rosin.

Paraflln. Candelilia wan...

, Menhade Examples 10 to 16 Example No.

Beeswax Montan wax Carnauba w x Castor oil Rapeseed nil Peanut o oil Corn oiL The polymerized rosin and the wax were melted together and heated to 150 C. and heldthere for 30 minutes whereupon the oily modifying agent was introduced The composition was stirred thoroughly and heated to 160 C. whereup a fab- 'ric tape. was immersed therein and thoroughly impregnated therewith, withdrawn and allowed to drain, The resulting electrical insulating tape exhibited properties which were much superior to those of an electrical insulating tape made with similar compositions wherein rosin was employed instead of polymerized rosin.

Example 17 Light current transformer coils of the type used in communication work were saturated in the usual way and then potted in a metal can withmolten polymerized rosin instead or ordinary rosin. Upon cooling, there was obtained a transiormer which was considerably better than a similar transformer potted in ordinary rosin.

Fmmthe foregoing, it will be seen that the 20 present invention gives rise to a number-oi advantages over the prior art electrical insulatingmaterials. Numerous other advantages of the electrical insulation of'the present invention will be apparent to those skilled irtthe art. It will be understood that the details and examples hereinbetore set forth are illustrative only and that the invention as broadly described and claimed is in no way limited thereby.

What I claim and desire to protect by Letters Patent is:

1. An electrical insulating composition comprising polymerizedrosin and gum accroides. .2. An electrical insulating composition comprising by weight approximately 44% of polyof castor oil, and 2% parts of stearic acid.

JOSEPH N. BbRGLIN.

merized rosin, 44% of gum accroides. 8% parts 

